It is usually husbands who crack the jokes about difficult, interfering mothers-in-law.

But their wives probably have more reason to complain.

A study of hundreds of families has found that mothers are far more likely to feud with a daughter-in-law than a son-in-law.

Nearly two-thirds of daughters-in-law accused their husband's mother of 'unreasonably jealous maternal love'.

A similar proportion of mothers-in-law complained they had been isolated and excluded by a female addition to the family.

Dr Terri Apter, a psychologist at Newnham College, Cambridge, has spent 20 years researching the type of battles seen in the film Monster-in-Law, starring Jane Fonda and Jennifer Lopez.

She interviewed 49 couples and 156 other people, and drew on past studies to compile her new book, What Do You Want From Me?

She said: 'As they struggle to achieve the same position in the family as primary woman, each tries to establish or protect their status, each feels threatened by the other.

'Mother-in-law and daughter-in-law conflict often emerges from an expectation that each is criticizing or undermining the other. But this mutual unease may have less to do with actual attitudes and far more to do with persistent female norms that few of us manage to shake off completely.'

These 'norms' include the fact that wives are still usually in charge of the cooking, cleaning and children's welfare - opening them up to criticism from an older woman who has done it all before.

And many women cannot break the habits of childhood, when they ousted rivals from playground cliques using subtle and indirect insults over extended periods of time. Dr Apter said one woman she spoke to began receiving messages from her mother-in-law-to-be two months before the wedding.

Jenny, 26, from North London, said one warned: 'My son thinks about me every day, every minute of the day, every second of every minute of the day.' Other letters were critical, intrusive or seeking pity.

Another interviewee, mother-in-law Annie, 64, from Yorkshire, said: 'My daughter-in-law is so cold towards me.

'She begrudges any time or attention my son gives to me and takes every opportunity to minimise the importance and depth of bond he and I have.'

女婿們常愛拿難纏多事的丈母娘開開玩笑。

而媳婦們可能有更多抱怨的理由。

一項針對數百個家庭的調查發現，婆媳關系比岳母和女婿的關系難處得多。

調查顯示，近三分之二的兒媳稱她們的婆婆“溺愛兒子，常常吃醋”。

另有相同比例的婆婆則抱怨由于兒媳的出現，她們被冷落了。

英國劍橋大學紐漢姆學院的心理學家特里•阿普特博士在過去20年中對婆媳沖突的類型進行了研究，由影星簡•芳達和詹妮佛•洛佩茲主演的電影《怪獸婆婆》就講述了婆媳之間針鋒相對的故事。

為編寫新書《想從我這里得到什么？》，特里博士對49對夫婦和另外156人進行了訪問，并借鑒了之前的一些研究成果。

她說：“婆婆和兒媳都爭當家庭中的女主人，她們都試圖建立和維護自己在家庭中的地位，雙方都感覺受到了對方的威脅。”

“婆媳沖突的原因通常是雙方都認為對方在指責或貶低自己。但這種互相看不慣與實際態度無關，而與我們都無法完全擺脫的“女性常規”緊密相連。

這些“常規”包括媳婦在家庭中仍負責做飯、打掃房間和照顧孩子等家務事，而在這些方面經驗豐富的婆婆難免會批評她們。

而且很多女性無法改掉兒時的習慣，女孩小時候通常會與對手長期地暗地里較勁以將她們擠出自己的小圈子。阿普特博士稱，一位受訪女性稱，她在結婚前兩個月就不斷地收到婆婆的來信。

來自倫敦北部的26歲的珍妮稱，她的婆婆在一封信中“警告”她說：“我的兒子每天、每分鐘、每秒鐘都在想我。”其他的信要么是指責叨擾，要么是尋求同情。

而另一位受訪者、來自約克郡的64歲的婆婆安妮說：“兒媳對我的態度十分冷漠。”

她說：“只要兒子和我在一起，或者關心我，她就不樂意。她還利用一切機會疏遠我和兒子的關系。”